Variola Virus

Encyclopedia of Espionage, Intelligence, and Security
COPYRIGHT 2004 The Gale Group Inc.

Variola Virus

█ JULI BERWALD

Variola virus (or variola major ) is the virus that causes smallpox. The virus is one of the members of the poxvirus group (Poxviridae ) and it is one of the most complicated animal viruses. The variola virus is extremely virulent and is among the most dangerous of all the potential biological weapons.

The variola virus particle is shaped like a biconcave brick 200 to 400 nm long. Its inner compartment contains a highly compressed double strand of deoxyribonucleic acid as well as about 100 proteins and 10 viral enzymes. The enzymes are used in nucleic acid replication. Variola DNA contains about 250,000 base pairs, which make up about 200 genes. The depressions in the brick shape contain structures called lateral bodies, whose function is unknown. Two layers of membrane surround the outside of the virus. The outer layer is covered with spikes 20 nm long that are sometimes arranged helically.

The variola virus attaches to membrane receptors on the exterior of the host cell. The exact mechanisms involved in the binding to and penetration of the host membrane are not known. As it enters the cell, however, the virus loses its exterior membrane coat. Once inside the cell the interior membrane layer is removed and the virus's proteins, enzymes and DNA are released into the cytoplasm of the host cell where viral replication and assembly takes place. The first step in replicating the virus DNA involves a particular set of virus enzymes called Type I topiosomerase enzymes, which uncoil the compressed strands of variola DNA and aid in replicated the early genes. The second step of genome replication involves replicating the late genes. During the replication of the variola DNA, large concatamers are formed and subsequently cleaved to form individual virus genomes. The variola virus appears to be able to replicate itself without using any of the host cell's replication machinery. Individual viruses are assembled with the help of the Type I topiosomerase enzymes. It is thought that viral membranes are taken from the cisternae between the host's Golgi apparatus and endoplasmic reticulum. As new viruses are released from the host cell, this Golgi derived membrane is traded for the host's cell membrane. Release occurs about 12 hours after initial infection. The production of variola virus by the host cell usually results in host cell death.

Variola virus infects only humans and can be easily transmitted from person to person via the air. Inhalation of only a few virus particles is sufficient to establish an infection. Transmission of the virus is also possible if items such as contaminated linen are handled. The common symptoms of smallpox include chills, high fever, extreme tiredness, headache, backache, vomiting, sore throat with a cough, and sores on mucus membranes and on the skin. As the sores burst and release pus, the afflicted person can experience great pain. Males and females of all ages are equally susceptible to infection. Prior to smallpox eradication approximately one third of patients died—usually within a period of two to three weeks following appearance of symptoms.

The origin of the variola virus in not clear. However, the similarity of the virus and cowpox virus has prompted the suggestion that the variola virus is a mutated version of the cowpox virus. The mutation likely allowed to virus to infect humans. If such a mutation did occur, then it is possible that when early humans became more agricultural and less nomadic, there may have been selective pressure for the cowpox virus to adapt the capability to infect humans.

Vaccination to prevent infection by the variola virus was established in the 1700s. English socialite and public health advocate Lady Mary Wortley Montagu popularized the practice of injection with the pus obtained from smallpox sores as a protection against the disease. This technique became known as variolation. Late in the same century, Edward Jenner successfully prevented the occurrence of smallpox by an injection of pus from cowpox sores. This was the first vaccination. Vaccination against smallpox has been very successful, and the variola virus is the only pathogenic virus that has been eliminated from the natural environment. The last recorded case of smallpox infection was in 1977. Routine vaccination against smallpox was discontinued in the 1980s.

In the late 1990s, a resolution was passed at the World Health Assembly directing that the remaining stocks of variola virus be destroyed to prevent the reemergence of smallpox and the misuse of the variola virus as a biological weapon. At the time only two high-security laboratories were thought to contain variola virus stock: the Centers for Disease Control and Prevention in Atlanta, Georgia, and the Russian State Center for Research on Virology and Biotechnology in Koltsovo, Russia. However, this decision was postponed until 2002, and now the United States government has indicated its unwillingness to comply with the resolution because of security issues related to potential bioterrorism. Destruction of the stocks of variola virus would deprive countries of the material needed to prepare vaccine in the event of the deliberate use of the virus as a biological weapon. This scenario has gained more credence in the past decade, as terrorist groups have demonstrated the resolve to use biological weapons, including smallpox. In addition, intelligence agencies in several Western European countries issued opinions that additional stocks of the variola virus exist in other than the previously authorized locations.

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Variola Virus

World of Microbiology and Immunology
COPYRIGHT 2003 The Gale Group Inc.

Variola virus

Variola virus (or variola major virus) is the virus that causes smallpox . The virus is one of the members of the poxvirus group (Family Poxviridae ). The virus particle is brick shaped and contains a double strand of deoxyribonucleic acid . The variola virus is among the most dangerous of all the potential biological weapons.

Variola virus infects only humans. The virus can be easily transmitted from person to person via the air. Inhalation of only a few virus particles is sufficient to establish an infection. Transmission of the virus is also possible if items such as contaminated linen are handled. The various common symptoms of smallpox include chills, high fever, extreme tiredness, headache, backache, vomiting, sore throat with a cough, and sores on mucus membranes and on the skin. As the sores burst and release pus, the afflicted person can experience great pain. Males and females of all ages are equally susceptible to infection. At the time of smallpox eradication approximately one third of patients died—usually within a period of two to three weeks following appearance of symptoms.

The origin of the variola virus in not clear. However, the similarity of the virus and cowpox virus has prompted the suggestion that the variola virus is a mutated version of the cowpox virus. The mutation allowed to virus to infect humans. If such a mutation did occur, then the adoption of farming activities by people, instead of the formally nomadic existence, would have been a selective pressure for a virus to adopt the capability to infect humans.

Vaccination to prevent infection with the variola virus is long established. In the 1700s, English socialite and public health advocate Lady Mary Wortley Montague popularized the practice of injection with the pus obtained from smallpox sores as a protection against the disease. This technique became known as variolation. Late in the same century, Edward Jenner successfully prevented the occurrence of smallpox by an injection of pus from cowpox sores. This represented the start of vaccination.

Vaccination has been very successful in dealing with variola virus outbreaks of smallpox. Indeed, after two decades of worldwide vaccination programs, the virus has been virtually eliminated from the natural environment. The last recorded case of smallpox infection was in 1977 and vaccination against smallpox is not practiced anymore.

In the late 1990s, a resolution was passed at the World Health Assembly that the remaining stocks of variola virus be destroyed, to prevent the re-emergence of smallpox and the misuse of the virus as a biological weapon. At the time only two high-security laboratories were thought to contain variola virus stock (Centers for Disease Control and Prevention in Atlanta, Georgia, and the Russian State Centre for Research on Virology and Biotechnology , Koltsovo, Russia). However, this decision was postponed until 2002, and now the United States government has indicated its unwillingness to comply with the resolution for security issues related to potential bioterrorism . Destruction of the stocks of variola virus would deprive countries of the material needed to prepare vaccine in the event of the deliberate use of the virus as a biological weapon. This scenario has gained more credence in the past decade, as terrorist groups have demonstrated the resolve to use biological weapons, including smallpox. In addition, intelligence agencies in several Western European countries issued opinions that additional stocks of the variola virus exist in other than the previously authorized locations.

See also Bioterrorism, protective measures; Bioterrorism; Centers for Disease Control (CDC); Smallpox, eradication, storage, and potential use as a bacteriological weapon; Viral genetics; Virology; Virus replication; Viruses and responses to viral infection

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Variola Virus

World of Forensic Science
COPYRIGHT 2005 Thomson Gale

Variola Virus

Variola virus (or variola major ) is the virus that causes smallpox . The virus is one of the members of the poxvirus group (Poxviridae ) and it is one of the most complicated animal viruses. The variola virus is extremely virulent and is among the most dangerous of all the potential biological weapons.

The variola virus particle is shaped like a biconcave (concave on both sides) brick about 200 to 400 nm (nanometers) long. Its inner compartment contains a highly compressed double strand of deoxyribonucleic acid as well as about 100 proteins and 10 viral enzymes. The enzymes are used in nucleic acid replication.

The variola virus attaches to membrane receptors on the exterior of the host cell. The exact mechanisms involved in the binding to and penetration of the host membrane are not known. As it enters the cell, however, the virus loses its exterior membrane coat. Once inside the cell, the interior membrane layer is removed and the virus's proteins, enzymes, and DNA are released into the cytoplasm of the host cell where viral replication and assembly takes place. The production of variola virus by the host cell usually results in host cell death.

Variola virus infects only humans and can be easily transmitted from person to person via the air. Inhalation of only a few virus particles is sufficient to establish an infection. Transmission of the virus is also possible if items such as contaminated linen are handled. The common symptoms of smallpox include chills, high fever, extreme tiredness, headache, backache, vomiting, sore throat with a cough, and sores on mucus membranes and on the skin. As the sores burst and release pus, the afflicted person can experience great pain. Males and females of all ages are equally susceptible to infection. Prior to smallpox eradication approximately one third of patients died—usually within a period of two to three weeks following appearance of symptoms.

The origin of the variola virus in not clear. However, the similarity of the virus and cowpox virus
has prompted the suggestion that the variola virus is a mutated version of the cowpox virus. The mutation likely allowed the virus to infect humans. If such a mutation did occur, then it is possible that when early humans became more agricultural and less nomadic, there may have been selective pressure for the cowpox virus to adapt the capability to infect humans.

Vaccination to prevent infection by the variola virus was established in the 1700s. English socialite and public health advocate Lady Mary Wortley Montagu popularized the practice of injection with the pus obtained from smallpox sores as a protection against the disease. This technique became known as variolation. Late in the same century, Edward Jenner successfully prevented the occurrence of smallpox by an injection of pus from cowpox sores. This was the first vaccination. Vaccination against smallpox has been very successful; the variola virus is the only pathogenic virus that has been eliminated from the natural environment. Routine vaccination against smallpox was discontinued in the 1970s and considered globally eradicated in 1980. The last recorded case of naturally occurring smallpox infection was in 1977 in Somalia, Africa.

see also Ebola virus; Pathogens; Smallpox.

Cite this article Pick a style below, and copy the text for your bibliography.

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Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

Notes:

Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.

In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.